Fire detecting apparatus sensitive to refraction

ABSTRACT

FIRE DETECTING APPARATUS COMPRISES A LASER, A PHOTOCELL WHICH ARE SPACED FROM EACH OTHER, THE PHOTOCELL BEING RESPONSIVE TO A STATE OF INCIDENCE OF THE LIGHT BEAM THEREON AND AN ALARAM AND/OR FIRE CONTROL APPARATUS FOR ACTIVATION IN RESPONSE TO A STATE OF NON-INCIDENCE OF THE BEAM ON THE DETECTOR. THE LASER AND PHOTOCELL ARE SO ARRANGED, E.G. SO THE LIGHT BEAM TAKES A PATH OF ZIG-ZAG CONFIGURATION, THE REFRACTION OF THE BEAM DURING ITS PASSAGE THROUGH THE SPACE IN THE PRESENCE OF FIRE PRODUCES THE STATE OF NONINCIDENCE OF THE LIGHT BEAM.

Feb. 23, 1971 D. l. I AwsoN 3,566,335

FIRE DETECTING APPARATUS SENSITIVE TOI REFRACTION med April 22, 196s United States Patent O 3,566,385 FIRE DETECTING APPARATUS SENSITIVE T REFRACTION Dennis Illingworth Lawson, Boreham Wood, England,

assignor to National Research Development Corporation, London, England, a British Corporation Filed Apr. 22, 1968, Ser. No. 723,139 Int. Cl. G08b 21/00 U.S. Cl. 340-228 4 Claims ABSTRACT 0F THE DISCLOSURE Fire detecting apparatus comprises a laser, a photocell which are spaced from each other, the photocell being responsive to a state of incidence of the light beam thereon and an alarm and/or fire control apparatus for activa tion in response to a state of non-incidence of the beam on the detector. The laser and photocell a-re so arranged, e.g. so the light beam takes a path of zig-zag conguration, that refraction of the beam during its passage through the space in the presence of lire produces the state of nonincidence of the light beam.

This invention concerns fire detecting apparatus.

According to the present invention, there is provided fire detecting apparatus comprising emitter means for generating a beam of electromagnetic radiation, detector means having an electromagnetic radiation sensitive surface surrounding an electomagnetic radiation sensitive surface surrounding an electromagnetic radiation insensitive surface, and fire control means for activation by the detector means, said emitter means and said detector means being so arranged that the passage of the beam between the emitter means and the detector means, in the absence of re in the space through which the beam passes, causes the beam to be incident upon the surface of the detector means which is radiation insensitive, and the fire control means to be non-activated, and that refraction of the beam during its passage through said space in the presence of re therein causes the beam to be incident upon the surface of the detector means which is radiation sensitive, and the re control means to be activated.

If a lire should occur in a space, the temperature of the air in the space will rise and various gases such as carbon dioxide will be evolved. The heated air and the heated gases will, however, have refractive indices which will vary spatially from that of the original air in the space which was at normal temperature. Thus refraction of the beam of electromagnetic radiation when passing through the space in which the lire has occurred will be observed.

In a preferred embodiment of the invention said one state in the absence of fire in the space is that of incidence of said beam on the detector means.

The one said state in the absence of lire in the space may be that of non-incidence of said beam on the detector means.

Preferably the -said electromagnetic radiation is in the substantially visible range of wavelengths.

Preferably at least one reflector is provided in said space so that the Ibeam is rellected during its passage through the space between the emitter means to the detector means.

The emitter means may be a laser. In addition the control means may comprise alarm means.

According to a further aspect of the invention there is provided tire detecting apparatus comprising a laser for generating a beam of electromagnetic radiation, the detector means having an electromagnetic radiation sensitive surface surrounding an electromagnetic radiation insensitive surface, a plurality of reectors positioned to direct radiation from said laser to said detector means in such a manner that the beam undergoes multiple reflections in its passage between the laser and detector means, and lire control means for activation by the detector means, said laser and said detector means being so arranged that the passage of the beam between the laser and the detector means, in the absence of fire in the space through which the beam passes, causes the beam to be incident upon the insensitive surface of the detector means, and the tire control means to be non-activated, and that refraction of the beam during its passage through said space in the presence of fire therein causes the beam to be incident upon the sensitive surface of the detector means and the lire control means to be activated.

The invention is illustrated, merely by way of example, in the accompanying drawing, in which FIG. 1 is a diagrammatic plan view of a lire detecting apparatus according to the present invention and FIG. 2 is part of a modified detector for use with the lire detecting apparatus of FIG. 1.

Referring to the drawing, a lire detecting apparatus comprises an emitter A which directs a beam of electromagnetic radiation across a space S. Successive reiiectors B to H which may, for example, be plate glass mirrors are placed in the beam path, shown by the dotted lines in the drawing, so that the beam is of zig-zag or criss-crossed form and substantially covers the space S to be protected from lire. There is provided a beam detector .I which, if the beam is in the visible range of wavelengths, may be a photocell.

It is preferred that the electromagnetic radiation be in the visible or near-visible range of wavelengths since such radiation can be more readily collimated and thereby employed over large areas by using reflection from reflectors. In this connection it is to be noted that a laser is particularly suitable for providing an intense highly collimated beam. By using an intense beam the detector I may be made unresponsive to natural or artiiicial light in the space to be measured without signilicantly decreasing the sensitivity of the apparatus. A focussing arrangement, such as a monocular may be placed in front of the emitter A to bring the beam to a point focus at the detector J to increase the sensitivity of the apparatus.

The system is so arranged that the beam is normally incident on the detector J, the detector J being effective to activate alarm and/or control means (not shown) in response to non-incidence of the beam by way of refraction through the effects of fire.

Alternatively, the converse arrangement may be ernployed whereby there will be non-incidence in the absence of fire, and activation arises with beam incidence on the detector by refraction.

However, the first arrangement is to be preferred since it inherently provides a fail-safe operation, and it can also give rise to a more compact and less complex system than the second arrangement and will operate if the beam is absorbed by smoke. In the rst arrangement, the detector need only be sufficiently large for incidence of the beam thereon in normal circumstances, including beam excursions arising from any effects of a safe nature, such a localised heating which may be reasonably anticipated. Any larger excursions, arising from lire or other unpredictable effects, will automatically give rise to detector activation. In the second arrangement, on the other hand as shown in FIG. 2, a similar result will only be achieved by way of an arrangement using a detector having an annular electromagnetic radiation sensitive surface P surrounding an electromagnetic radiation insensitive surface Q. In the presence of lire the beam which is the absence of lire is incident upon the insenitive surface, is deflected on to the sensitive surface.

On activation of the detector, alarm means, such as of audible and/ or visible form operated locally or remotely of the area in question, may be set off and/or re control means such as a sprinkler system may be brought into action. It Will be seen that, in the simplest form of such a system, the beam generator and the detector will be mutually facing along a rectilinear beam path. The area which is surveyed in this case will, of course, conform generally to the beam path. While this may be satisfactory for some applications, lire in a region laterally remote from the beam path will not be detected as a result of beam refraction until a significant spread of the lire has occurred. This can, of course, be taken into account by use of a number of systems having at least partly common alarm and/ or fire control means in association with an area to be protected such as of the more usual rectangular room or building conguration. Additionally a re in the proximity of the detector will cause the beam to be refracted less than a re in the proximity of the emitter by the optical lever etfect. Thus, the use of reflectors to produce a beam path of Zig-zag or criss-cross form, as shown in the drawing, elects economy of the system and is preferred.

1. Fire detecting apparatus comprising emitter means for generating a beam of electromagnetic radiation, detector means having an electromagnetic radiation sensitive surface surrounding an electromagnetic radiation insenitive surface, and re control means for activation by the detector means, said emitter means and said detector means being so arranged that the passage of the beam between the emitter means and the detector means, in the absence of re in the space through which the beam passes, causes the beam to be incident upon the surface of the detector means which is radiation insensitive, and the tire control means to be non-activated, and that refraction of the beam during its passage through said space in the presence of re therein causes the beam to be incident upon the surface of the detector means which is radiation sensitive, and the lire control means to be activated.

2. Apparatus as claimed in claim 1 in which said emitter means is a laser.

3. Apparatus as claimed in claim 2 in which said re control means comprise alarm means.

4. Fire detecting apparatus comprising a laser for generating a beam of electromagnetic radiation, detector means, the detector means having an electromagnetic radiation sensitive surface surrounding an electromagnetic radiation insensitive surface, a plurality of reflectors positioned to direct radiation from said laser to said ldetector means in such a manner that the beam undergoes multiple reilections in its passage between the laser and detector means, and re control means for activation by the detector means, said laser and said detector means being so arranged that the passage of the beam between the laser and the detector means, in the absence of re in the space through which the beam passes, causes the beam to be incident upon the insensitive surface of the detector means, and the re control means to be nonactivated, and that refraction of the beam during its passage through said space in the presence of fire therein causes the beam to be incident upon the sensitive surface of the detector means and the re control means to be activated.

References Cited UNITED STATES PATENTS 2,181,173 2/1938 Martin et al 356-207X 3,051,281 8/1962 Hul, Jr. 250218X 3,075,426 1/1963 Robinson Z50-218K 3,098,932 7/1963 Laudon 250-218X 3,447,370 6/1969 Tanzman 250-2l8UX 2,886,715 4/1960 Broerman et al 250-218 FOREIGN PATENTS 658,811 l 3/1938 Germany 340-237 JAMES W. LAWRENCE, Primary Examiner lC. M. LEEDN, Assistant Examiner U.S. Cl. X.R. 

